The spray characteristics of a newly developed Y-jet-type airblast atomizer which embeds a fluid amplifier to control a mean droplet diameter automatically were measured. The fluid amplifier has a high reliability and high durability since it has no moving part to control the liquid flow. The newly developed atomizer has two kinds of ports, that is, smaller port which has smaller inner diameter and larger port which has larger inner diameter. Fine droplets are ejected from the smaller port, and relatively coarse droplets are ejected from the larger port. The fluid amplifier controls the liquid distribution to two kinds of ports so that as the total liquid flow rate increases the liquid flowing into smaller ports increases relatively. It was found that the bistable amplifier is suitable to adjust the liquid distribution to respective ports. Sauter mean diameter stays within the accuracy of twenty microns in the present experimental range of liquid flow rate and atomizing air flow rate. Comparing the atomizers which have different inner diameters of larger port, the mean diameter decreases with decrease of the inner diameter. On the other hand, by the experiments using the atomizers which have the same inner diameter and the different length of larger port, minimum mean diameter was obtained by the atomizer with L/D of around 2.0.